The present invention relates to fluorinated organic compounds that self-assemble to form monolayers, and in particular to fluorinated phosphonic acids.
Self-assembling materials, as their name implies, spontaneously form a structure (e.g., micelle or monolayer) when they contact another substance. Monolayer formation is particularly useful when it occurs on the surface of a solid substrate (e.g., a piece of metal). If a monolayer is formed from a material that imparts a low surface energy to a surface of a substrate, then one or more useful properties such as water repellency, corrosion resistance, lubricity, and adhesive release may be imparted to that surface. If the surface energy is low enough, oil repellency and soil (i.e., stain) resistance may be achieved. Generally, surface energies this low may be achieved through use of fluorocarbon materials.
Fluorinated self-assembled monolayers have been employed in soil resistant coatings, anti-reflective glass coatings, and release coatings. Typical self-assembling materials consist of a polar head group attached to a hydrophobic tail. Despite their relatively higher cost, self-assembling materials having a fluorinated tail have gained wide acceptance in industry. This is because they typically substantially outperform alternative materials, such as those having a hydrocarbon or silicone tail, for example, in terms of adhesive release and soil resistance. Commercial products in this area have typically utilized materials bearing seven- and eight-carbon perfluoroalkyl groups. Recently, there has been a significant effort in industry to find alternative materials to such groups.
It would be desirable to have new materials that self-assemble to form monolayers having low surface energies on a wide range of substrates, and it would be especially desirable that such materials not contain seven- and eight-carbon perfluoroalkyl groups.
In one aspect, the present invention provides a fluorinated phosphonic acid compound having the formula: 
wherein:
R1 is a straight chain alkylene group having from about 3 to about 21 carbon atoms, an oxa-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms, or a thia-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms;
R2 is a perfluoroalkyl group having from about 4 to about 10 carbon atoms;
R3 is hydrogen, an alkali metal cation, or an alkyl group having from about 1 to about 6 carbon atoms; and
M is hydrogen or an alkali metal cation, with the proviso that if R1 is an unsubstituted straight chain alkylene group, then the sum of carbon atoms in R1 and R2 combined is at least 10.
In another aspect, the present invention provides a method of treating the surface of an article, the method comprising:
providing a substrate having a surface; and
applying a fluorinated phosphonic acid compound to the surface of the substrate, the compound having the formula: 
wherein:
R1 is a straight chain alkylene group having from about 3 to about 21 carbon atoms, an oxa-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms, or a thia-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms;
R2 is a perfluoroalkyl group having from about 4 to about 10 carbon atoms;
R3 is hydrogen, an alkali metal cation, or an alkyl group having from about 1 to about 6 carbon atoms; and
M is hydrogen or an alkali metal cation, with the proviso that if R1 is an unsubstituted straight chain alkylene group, then the sum of carbon atoms in R1 and R2 combined is at least 10.
In another aspect, the present invention provides an article comprising a substrate having a surface, the surface intimately contacting at least a partial monolayer of a fluorinated phosphonic acid compound having the formula: 
wherein:
R1 is a straight chain alkylene group having from about 3 to about 21 carbon atoms, an oxa-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms, or a thia-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms;
R2 is a perfluoroalkyl group having from about 4 to about 10 carbon atoms;
R3 is hydrogen, an alkali metal cation, or an alkyl group having from about 1 to about 6 carbon atoms; and
M is hydrogen or an alkali metal cation, with the proviso that if R1 is an unsubstituted straight chain alkylene group, then the sum of carbon atoms in R1 and R2 combined is at least 10.
In another aspect, the present invention provides an article prepared by a process, the process comprising:
providing a substrate having a surface; and
applying a fluorinated phosphonic acid compound to the surface of the substrate, the compound having the formula: 
wherein:
R1 is a straight chain alkylene group having from about 3 to about 21 carbon atoms, an oxa-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms, or a thia-substituted straight chain alkylene group having from about 2 to about 20 carbon atoms;
R2 is a perfluoroalkyl group having from about 4 to about 10 carbon atoms;
R3 is hydrogen, an alkali metal cation, or an alkyl group having from about 1 to about 6 carbon atoms; and
M is hydrogen or an alkali metal cation, with the proviso that if R1 is an unsubstituted straight chain alkylene group, then the sum of carbon atoms in R1 and R2 combined is at least 10.
Fluorinated phosphonic acids of the present invention self-assemble (e.g., forming monolayer films) when applied to a wide variety of substrates, resulting in coatings on the substrates that exhibit at least one of low surface energy, adhesive release, lubricity, water repellency, and/or soil resistance.
As used herein:
xe2x80x9cperfluoroxe2x80x9d refers to the exhaustive substitution of hydrogen by fluorine in the group or molecule to which it refers.